The present invention relates to packaging films, and more specifically to packaging films useful in vacuum packaging applications.
Vacuum packaging, and particularly vacuum skin packaging has become an increasingly attractive way of packaging fresh red meats. The final package presents a tight fitting, clear package which protects the food article from the external environment. However, the demands imposed on the packaging material used in vacuum packaging, and especially in vacuum skin packaging, are high.
Two particular characteristics which are especially desirable in vacuum skin packaging applications, especially in the packaging of fresh beef, pork, broiled and browned pork, shingled turkey breast, and other meat items, are implosion or breakage resistance and shelf life.
Generally, products that have cavities or undercuts are especially prone to implosions or leakers created by failure of the film during the vacuum skin packaging process. Using standard materials, package failures as high as 60% have occurred. Thus, in actual practice, conventional films tend to be broken when subjected to the high stretch ratios and particular projections, undercuts or recesses present on the material being packaged.
At the same time, high oxygen barrier characteristics are required in packaging material where the product to be packaged is sensitive to and degrades in the presence of oxygen. Fresh red meat products in particular typically require packaging materials with high oxygen barrier properties in order to insure adequate or extended shelf life during storage, distribution and retail display under high humidity conditions.
The vacuum skin packaging process itself is now well known in the art. The packaging material generally comprises a top web and a bottom web which are each sent to the packaging station. The meat or other food to be packaged is placed onto the bottom web before the packaging station. The upper web comprises a film of a thermoplastic material which is optionally preheated and then fed to the packaging station and over the product on the bottom web. There it is usually heated by contact with a heated member, for instance the inner surface of a "dome". The space between the top and bottom webs around the food is then evacuated and the top web is allowed to come into contact with the bottom web and with the food. The top web may be held against the dome for instance by vacuum pressure which is released when it is desired to allow the top web to come into contact with the bottom web. Sealing of the top and bottom webs is achieved by a combination of heat from the dome and pressure difference between the inside of the package and the outside atmosphere and can be aided by mechanical pressure and/or extra heating. The heat that is supplied in the process is merely to allow the web to form and take up the form of the food product being packaged.
Skin packaging and particular developments of it are further described in European patent publication 243510 (Botto et al) disclosing a coextruded multilayer film having the structure ionomer/EVA (18%)/adhesive/EVOH/EVA (18%)/high density polyethylene. The film in this disclosure is useful in vacuum packaging food products. "EVOH" here represents ethylene vinyl alcohol copolymer. "EVA" here represents ethylene vinyl acetate copolymer. Several similar structures are also disclosed in the Botto et al reference.
It is an object of the present invention to provide a packaging material useful in vacuum packaging and especially vacuum skin packaging applications.
It is a further object to provide such a material which has good resistance to implosion or breakage, good formability, combined with extended shelf life for food products such as fresh red meat products.